In a network system including network devices, for example, a multiprotocol label switching (MPLS) network or an Internet Protocol (IP) network, a link aggregation (LAG) technology may be used for the network devices to improve reliability. Link aggregation refers to logically combining at least two single links into one aggregated link. A bandwidth of an aggregated link is equal to a sum of bandwidths of multiple links included in the aggregated link. Therefore, performance of the aggregated link is better, and load sharing may be performed between different links in the aggregated link. When one or more links in the aggregated link are faulty, communication between devices coupled using the aggregated link is not interrupted.
In the prior art, fault detection is performed on an aggregated link using bidirectional forwarding detection (BFD). The BFD can be used to detect whether a path between two network devices is faulty, including whether a port is faulty, whether a link is faulty, whether the network devices are faulty, and the like. When only one BFD session is used to detect whether the aggregated link is faulty, a misjudgment easily occurs.